Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 From altimetry to operational oceanography, need for a precise geoid. Exemple of the E.U. GOCINA Project. Outline  Use of satellite altimetry for oceanography  Operational oceanography – GODAE - MERCATOR  Mean dynamic topography (absolute dynamic topography): the present  Conclusions - perspectives for GOCE  The GOCINA project Fabrice Hernandez and P.Y. Le Traon CLS Space Oceanography Division + GOCINA consortium

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 Absolute dynamic topography from altimetry (1) 1.Estimate a mean dynamic topography ( ) from GOCE, altimetry or other: difference between MSS and geoid climatology from in situ data, or synthetic geoid product ocean model mean The mean should correspond to a mean over a precise time period determined by the sea level anomaly calculation (typically several years or the duration of an altimetric mission). The longer is the time period, the better as the scales of the mean signal will be larger. 2. Add this mean dynamic topography to sea level anomaly (  ') derived from repeat-track analysis. One of the main objectives of GOCE is to provide a sufficiently accurate geoid to allow a precise estimation of absolute dynamic topography from altimetry. In practice the best procedure to get an estimation of the absolute dynamic topography (and its error) (  = +  ') from altimetry will be : G  ’= h ’ G h  + G h’= h -

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 Absolute dynamic topography from altimetry (2) This product will have a major impact on scientific and operational applications (e.g. GODAE, MERCATOR) of satellite altimetry (e.g. Woodworth et al., 1998; Le Provost et al.,1999) : better interpretation of altimeter signals (absolute dynamic topography): Sea level monitoring and climate studies… comparison/combination with in-situ data general circulation and heat transport data assimilation and ocean forecasting... The (main) product that oceanographers will need from GOCE will thus be a mean dynamic topography (and its error)

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 Operational oceanography The GODAE vision "A global system of observations, communications, modelling and assimilation, that will deliver regular, comprehensive information on the state of the oceans, in a way that will promote and engender wide utility and availability of this resource for maximum benefit to the community” (GODAE Strategic Plan, 2001)

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The Global Oceanic Data Assimilation Experiment operational Objective: To provide a practical demonstration of real- time operational global oceanography  Regular comprehensive description of the ocean circulation at high temporal and spatial resolution  Consistent with a suite of remote and in-situ measurements and appropriate dynamical and physical constraints Climate and seasonal forecasting, marine safety, fisheries, the offshore industry, Navy applications and management of shelf/coastal areas are among the expected beneficiaries of GODAE The integrated description of the ocean that GODAE will provide will also be highly beneficial to the research community Includes the main operational and research institutions from Australia, Japan, United States, United Kingdom, France and Norway Main demonstration phase : 2003 to 2005 (prototypes are already running)

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 n In 2003, the modeling/assimilation unit of the MERCATOR system is based on two components : a high resolution (1/15°) North Atlantic model, including the Mediterranean sea an intermediate resolution (1/4°) Global Ocean model Common boundary : 9° N Atlantic

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 Forecasts for May 14, 2003 SSH 2003: the second MERCATOR Prototype : PSY2 Mixed layer depth

Meeting French Ressources Organization for GOCE Paris, the 14th of may, floats providing T and S profiles ( m) every 10 days and measuring velocity at 2000 m = vertical description large scale and seasonal variations water masses improved estimation of absolute mean dynamic topography (a few cm rms) …

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 SSALTO/DUACS (CLS/CNES) : Real time processing of TOPEX/POSEIDON, ERS-1/2, GFO, Jason-1 and ENVISAT Real time processing (2-3 days) Global crossover minimizations, inverse techniques to remove long wavelength errors => high accuracy SSH (Sea Surface Height) data Consistent mean profiles to reference multiple altimeter data => consistent SLA (Sea Level Anomaly) data Products directly useable for scientific and operational applications (climate and mesoscale) Real time processing of T/P and ERS-2 data during the 1998 El Nino Serving operational oceanography (GODAE) and climate forecasting centers Mesoscale to climate, surface integrated circulation

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 SSALTO/DUACS : High resolution from T/P, ERS-2 and GFO data + synthetic mean dynamic topography Need for operational oceanography: Maps of SLA can be produced with a good accuracy (better than 5cm and 10 cm/s) and describe scales shorter than 100 km and 5 days. The (main) product that oceanographers will need from GOCE will thus be a mean dynamic topography (and its error) at equivalent scale and accuracy !

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 Mean Dynamic Topography from POCM, Levitus and EGM96-MSS rms differences are about 12 cm (wavelengths > 2000 km) POCM EGM96 - MSS Levitus (700 m)

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 m m MSS CLS01 – EIGEN2 Levitus (700 m) OCCAM

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 Mean Dynamic Topography (conclusion…) Improvements needed in both accuracy and resolution… Based on CHAMP, GRACE, GOCE (large and medium scales), in-situ data and models (shortest scales, and consistent physics) Homogeneous period...

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 Improvement in the 7-day sea level anomaly forecast due to the use of a “GCE” MDT (Dombrowsky, 1999). Units from 0 to 50 cm 2 Use of a “GOCE” MDT allow a better prediction of the eddy field, by about 15% of the signal variance for a 7-day prediction. 2-week forecast error with “GOCE” MDT is equivalent to 1-week forecast error with “today” MDT This improvement will come in addition to the improvement in the knowledge of the mean circulation itself. The effect should be larger for longer term forecast Need for operational oceanography: Impact of GOCE and high accuracy MDT

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 Impact of the Synthetic MDT (Rio, 2003) in MERCATOR Synthetic MDTMERCATOR MDTDifference More realistic (comparison to drifter, hydrographic observations) Enhance the forecasting capability of the system?

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 MKE comparison (cm 2 /s 2 ): stronger mean currents. Subpolar gyre better defined 6 months of the impact experiment (operational configuration … Sept 01 to April 02) Impact of the Synthetic MDT (Rio, 2003) in MERCATOR

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 EKE comparison (cm 2 /s 2 ): intensification of the model mesoscale variability 6 months of the impact experiment (operational configuration … Sept 01 to April 02) Impact of the Synthetic MDT (Rio, 2003) in MERCATOR

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic GOCINA will develop generic tools to enhance ocean analysis using Earth observation data from ENVISAT and GOCE. The project will examine the mass and heat exchange across the Greenland-Scotland Ridge. This analysis will give invaluable information on the ocean role in climate. The project will in particular support the GOCE mission with a set of specific recommendation for integrating GOCE in ocean circulation studies and an accurate geoid model for validation purposes. A major task is to determine an accurate geoid in the region between Greenland and the UK and, thereby, create a platform for validation of future GOCE Level 2 data and higher order scientific products. The new and accurate geoid is used together with an accurate mean sea surface to determine the mean dynamic topography. The mean dynamic topography is used for improved analysis of the ocean circulation and transport through the straits between Greenland and the UK. Gocina: 36 mois (11/ /2005)

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic Partner 1 (KMS):Kort & Matrikelstyrelsen Geodetic Department, DK-2400 København Att: Per Knudsen (coordinator) Partner 2 (NMA):Norwegian Mapping Authority Geodetic Institute, N-3504 Hønefoss Att: Dag Solheim Partner 3 (UEDIN):The University of Edinburgh Geography and Geophysics, EH9 3JW Edinburgh Att: Roger Hipkin Partner 4 (UREADES):University of Reading Environmental Systems Science Centre, RG6 6AL Reading Att: Keith Haines Partner 5 (NERSC):Nansen Environmental and Remote Sensing Center N-5059 Bergen Att: Johnny Johannessen Partner 6 (CLS):Collecte Localisation Satellites Space Oceanography Division, F Ramonville St. Agne Att: Fabrice HernandezKMSPer KnudsenNMAUEDINUREADESNERSCCLS The partners each have a high international reputation for expertise relevant to their specific roles. KMS, NMA, and UEDIN have expertise in geodetic disciplines associated with geoid determination. UREADES, NERSC, and CLS have expertise in oceanographic disciplines associated with ocean circulation and data assimilation. KMS and CLS have expertise in processing satellite altimetry for both geodetic and oceanographic purposes.KMSNMA UEDIN UREADESNERSCCLSKMSCLS Strong collaboration with OCTAS (Norway)

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic WP1: Geoid determination (R. Forsberg/R. Hipkin) Collect marine gravity data Complete with air-borne gravity survey + intercalibration Compute gravimetric geoid + errors using state-of-the-art method (marine, land, topo, airborne data) with the mgal precision Take into account available CHAMP & GRACE data to enhance long wavelength.

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic Airborne gravimetry (collaboration with OCTAS)

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic WP2: Mean Sea Surface Determination (O. Andersen/F. Hernandez) Compile satellite altimetry: T/P, Jason-1, ERS-1/2, EnviSat, Geosat, GFO up to 2002 Analyse existing MSS in the area (KMS01, CLS01, GSFC00.1) Determine a high resolution MSS (1/60°).

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic WP3: Mean dynamic topography determination (K. Haines/F.Hernandez) Collect existing MDT (climatology, model, etc…) and evaluation Compile in-situ data (hydrographic data, surface drifters etc…) Determine a MDT from climatology Determine a synthetic MDT Determine a model MDT from OGCM.

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic WP4: Assessment and Validation (D. Solheim/A. Vest) To assess the initial models residuals Compare the different MDT to in-situ data Infer error characteristics of the different models.

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic MDT = KMS-01 MSS - ”Tallinn” geoid OCCAM MDT = KMS-01 MSS – EGM96 geoidMDT = KMS-01 MSS – geoid36.eig

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic MDT = KMS-01 MSS - ”Tallinn” geoid OCCAM MDT = KMS-01 MSS – EGM96 geoidMDT = KMS-01 MSS – geoid36.eig

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic WP5: Technique integration (R. Hipkin) Integrate the three quantities (MSS, MDT, geoid) and errors Testing new techniques (data assimilation and geoid inversion) for calculating the best possible local solution Investigate impact of the GOCE errors WP6: Ocean circulation and transport (F. Hernandez/J. Johannessen) Testing the MDT in OGCMs (impact in mass and heat transport across the straits, outflow…) Testing the predictability at seasonal/interannual scales (NAO prediction) WP7: Recommendations for integrating GOCE (J. Johannessen) Educate and prepare the community in using GOCE data for oceanography including sea level and climate research as well as operational prediction Develop methods for generating regional gravity fields and use them to generate a best possible regional gravity field and geoid model for the North Atlantic that can be used in validation of the GOCE products.

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 The GOCINA project (5th E.U. FP) Geoid and Ocean Circulation in the North Atlantic … If GOCE is launched in 2006, the GOCINA would be finished, but conclusions could be applied GOCINA is a unique community (geodesy and oceanography) for calibration and validation Direct outcome and applications for several communities (climate prediction, ocean studies, operational oceanography, marine security and oil industry…)